Along the development of mobile communication technology and technology for manufacturing mobile terminals, e.g., a mobile computer and a personal digital assistant (PDA), the Internet is applied to the next-generation wireless technology in support of mobility. Current wired Internet connection which is adopted in offices and schools is changed into wireless communication of 802.11 or wireless communication using Bluetooth or infrared communication.
Herein, 802.11 is a collection of specifications for wireless Local Area Network (LAN) developed by an Institute of Electrical and Electronics Engineers (IEEE) working group.
Generally, a wireless LAN is technology that replaces the wired environment from a hub to a subscriber end into wireless environment which is favorable for set up and mobility in the construction of a network.
The wireless LAN has an advantage that a network can be built in a short time compared to a wired LAN, because the wireless LAN uses radio frequencies from access point (AP) equipment to a mobile node (MN), instead of using cable to build the network. It also has an advantage that it is not limited to a fixed desktop environment and, it makes it possible to perform communication with a laptop computer and a personal computer (PC) card, while a user is moving.
At present, portable mobility is provided to work sites by mounting a wireless LAN card in a laptop computer, and the demand for the portable mobility is increasing. Besides, a variety of Internet Protocol (IP)-based services appear in a mobile communication system, which also increases a demand for an IP mobility service.
FIG. 1 is a block diagram showing a network where a user accesses to the Internet by using a wireless LAN. The present invention is applied to the network of FIG. 1.
As shown in FIG. 1, the network to which the present invention is applied includes the Internet 10, access routers 21 and 22, access points 31, 32, 33 and 34, and mobile nodes 40.
As shown from the arrows of FIG. 1, if the mobile node 40 moves from the current access point 32 area to another access point 33 area, the mobile node 40 determines whether there is handover from the current access router 21 and if it is determined that there is handover, a handover process is carried out by acquiring layer 3 information on the access router 22 of a new area.
Diverse data link layer technologies supporting wireless communication including 802.11 can be used for the layer 2 of a mobile node using mobile IPv6.
In the 802.11 wireless LAN environments which is used most commonly at present, a laptop computer or a PDA equipped with a wireless LAN card perform layer-2 communication with an access point that plays a role of a base station in a cellular system. In the Windows operating system or a wireless LAN card driver module of Linux, it determines re-establishment to a new access point by periodically checking the intensity of signals with the access point.
Meanwhile, the Internet Engineering Task Force (IETF) standardizes the mobile IP technology which supports mobility in addition to the existing IP technology. Herein, the IETF is a body that defines standards of Internet operating protocols such as Transmission Control Protocol/Internet Protocol (TCP/IP). The standards are presented in the form of Requests for Comments (RFC).
The design purpose of the mobile IPv6 is to provide mobility while using the functions of the IPv6. The mobile IPv6 provides the mobility more effectively than the mobile IPv4 and excellent extensibility.
That is, the mobile IPv6 can form location information of a mobile node automatically by using a neighbor discovery function and an address auto-configuration function, when the mobile node moves to a new network area. It also removes some signal messages and agents which should exist in the IPv4 by defining a new destination option to inform the location information on its movement to the new node in need of its location information. In addition, it provides a protocol for route optimization as a basic function.
However, the mobile IPv6 has as long delay time in the handover process, which is formed of a movement detection process for detecting that the mobile node is moved to a new network area, a new CoA configuration process, and a Duplicate Address Detection (DAD) process for checking the uniqueness of the newly generated address, affects a real-time service or other delay-sensitive services.
Herein, the CoA is a routable address of a mobile node having a subnet prefix of the new network, when the mobile node is moved to another network.
Therefore, the IETF has developed several handover mechanisms to reduce the time delay during handover, and one of them is mobile IPv6 fast handovers for which is dealt with in the mobile IP working group (Mobileip WG) of the IETF.
FIG. 2 is a flowchart describing the mobile IPv6 fast handovers of the IETF which is defined in the mobile IPv6 IETF fast handovers for standard documents.
First, if the mobile node 40 moves to a wireless LAN area of the new access router 22, at step 11, the mobile node 40 transmits a Router Solicitation for Proxy Advertisement (RtSolPr) message to the current access router 21 to perform handover from the current access router 21 to the new access router 22.
At step 12, the current access router 21 which receives the RtSolPr message adds a new CoA to be used in the new network to a Proxy Router Advertisement (PrRtAdv) message and transmits it to the mobile node 40. Then, at step 13, it transmits a Handover Initiate (HI) message containing the new CoA and the current CoA of the mobile node 40 to the new access router 22 which is the object of the handover.
Also, it prepares to perform packet forward or packet tunneling to send a packet taking the current CoA of the mobile node 40 as a destination address to the access router 22 which is the object of the handover.
Meanwhile, at step 14, the access router 22, which is the object of the handover and receives the HI message, checks whether the new CoA of the mobile node 40 is available and transmits a HACK message in response to the checking result. If Uflag is set up in the HI message, packets transmitted from the current access router 21 begin to be buffered.
In tunneling, the source address of external packets is the address of the current access router 21 and the destination address is the new access router 22 which is the object of the handover.
Meanwhile, at step 15, the mobile node 40 which receives the PrRtAdv message transmits F-BU message to the current access router 21 in response to the PrRtAdv message. The F-BU message is the final message transmitted from the current access router 21 area before the mobile node 40 performs layer 2 handover. The current access router 21 which receives the message begins to forward packets or perform tunneling.
At step 16, the current access router 21, which receives the HACK message, transmits an F-BACK message on whether the HACK message is to be used as a new CoA of the mobile node 40 to the mobile node 40. The message can be transmitted to the new access router.
Meanwhile, if the new CoA cannot be used in the new access router 22, the mobile node 40 receives an RA (Router Advertisement) message which is used in the new access router 22 area by using the current CoA and performs the general processes of mobile IPv6 CoA acquisition and binding.
If the mobile node 40 does not receive the F-BACK message from the current access router 21, it performs layer-2 handover into the new access router 22 area. After the mobile node 40 accesses to the access point of the new access router 22, at step 17, it transmits an F-NA message to the new access router 22 regardless of whether the F-BACK message is received, after the mobile node 40 accesses to the access point of the new router 22.
After the mobile node 40 accesses to the access point of the new router 22, layer 2 link up trigger is caused in the access point. The new access router 22 which receives the layer 2 link up trigger replaces it with F-NA. Herein, packets buffered in the new access router 22 are transmitted to the mobile terminal 40. If there is no link up trigger, the F-NA message performs the function instead.
Meanwhile, the new access router 22 which receives the F-NA message transmits an F-NA acknowledge message and inform the mobile node 40 of whether the new CoA is available or not. If the new CoA is available, the mobile node 40 performs the general mobile IPv6 binding process by using the address. Otherwise, if the new CoA is not available, the mobile node 40 receives a Router Advertisement (RA) message and performs the general process of mobile IPv6 CoA acquisition and binding based on the address.
Therefore, in order to perform the mobile IPv6 fast handovers of the IETF, messages including the Router Solicitation for Proxy Advertisement (RtSolPr), Proxy Router Advertisement (PrRtAdv), Handover Initiate (HI), Fast Binding Update (F-BU), Fast Binding Acknowledgement (F-BACK) messages should be realized additionally and the problem is that their operation processes are complicated.
Also, many mechanisms for performing fast handover researched in the IETF mobile IP working group are suggested to reduce delay in one area among three areas, which are movement detection, new CoA configuration, and binding update. The mobile IPv6 fast handovers, which is in progress as the current IETF mobile IP working group document is technology that reduces the entire handover delay time in the layer 3 by quickly detecting movement and configuring a new CoA based on handover expectation information in the layer 2.
In short, it supports real-time service by performing part of the layer 3 handover or delaying layer 3 registration by using a bidirectional tunnel based on the handover expectation information in the layer 2 to minimize the delay in handover before the layer 2 handover is completed. However, this method, too, has a problem that it is hard to obtain expectation information of the new network area by using the information of the layer 2 before the mobile node 40 moves to the new network area.